1. Field of the Invention
The present invention relates to a packet distributing device (for example, a router) for distributing packets of different priorities to a plurality of links of different qualities in accordance with the priorities of the packets.
2. Description of the Related Art
There are communication services that provide a plurality of links of different qualities between two endpoints; NTT's ATM MegaLink Extra Class Service and a multi-link service that bundles a plurality of lines into a single line are examples of such services. In such services, packets to be transmitted are assigned priorities according to the content or significance they represent, and packets of higher priority are transmitted on higher quality links and packet of lower priority on lower quality links, that is, each packet is always sent out on a link predetermined according to the priority assigned to the packet, so that packets of different priorities are not transmitted in a mixed fashion on the same link. In the ATM MegaLink Service, automatic switching is performed in the event of a link failure; in that case also, packets are always sent out according to the preassigned priority, and packets of different priorities do not use the same link.
With the prior art method that transmits packets always on predetermined links, if the number of packets assigned lower priority is quite large compared with the number of packets assigned higher priority, packet overflow may occur because the usage of the lower quality link becomes extremely high while the usage of the higher quality link is very low. Thus, in the prior art, a situation can occur where efficient use of the higher quality link cannot be made when enough capacity is left on the high quality link. Further, in a network that provides a plurality of links of different qualities, with provisions made for automatic switching to the next lower quality link in the event of a link failure, there arises the problem that when the switching is made, transmission of the lowest priority packets that use the lowest quality link cannot be effected at all.